1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a semiconductor device and, more particularly, to a semiconductor device using magnetic domain wall movement and a method of manufacturing the same.
2. Description of the Related Art
Data storing devices are divided, for the most part, into volatile data storing devices that lose all recorded data when power is turned off and non-volatile data storing devices that keep data even when power is turned off.
Non-volatile data storing devices include a hard disc drive (HDD) and a non-volatile random access memory (RAM). The HDD includes a read and write head and a rotating data recording medium, and can store data of 100 gigabites or more. However, a device that has a rotating part like the HDD has a problem in that it wears down over time, and thus, there is a high possibility of operational failure, thereby reducing reliability.
Therefore, as a method of solving the drawbacks of the conventional non-volatile data storing devices as described above, much research and development with respect to a new data storing device that uses a magnetic domain wall movement has been carried out.
A magnetic domain in a magnetic substance and magnetic domain walls will now be described. Afterwards, a storing device that uses the magnetic domain and the magnetic domain walls will be described.
A minute magnetic region that constitutes a ferromagnetic body is named as a magnetic domain. The rotation of electrons in a magnetic domain, that is, the direction of magnetic moment is identical. The size and magnetization direction of a magnetic domain can be appropriately controlled by the shape, size and properties of a magnetic substance and external energy.
A magnetic domain wall is a boundary portion of a magnetic domain having a magnetization direction different from another magnetic domain. The magnetic domain wall can be moved by an external magnetic field or by a current applied to a magnetic substance.
The principle of the magnetic domain wall movement can be applied to data storing devices such as HDDs. That is, an operation of reading/writing data is possible when the magnetic domains magnetized so as to correspond to specific data in a magnetic substance are moved in order to pass through a read/write head. In this case, a reading/writing operation is possible without directly rotating a recording medium. Accordingly, the problems of wearing down and failure of conventional HDDs can be solved. An example of a data storing device to which the principle of magnetic domain wall movement is applied has been disclosed in U.S. Pat. No. 6,834,005 B1.
Also, the principle of magnetic domain wall movement can be applied to a memory such as a non-volatile RAM. That is, a non-volatile memory device that can write/read a data ‘0’ or ‘1’ can be realized using a principle whereby a voltage in a magnetic substance varies according to the movement of magnetic domain walls in the magnetic substance having magnetic domains magnetized in a specific direction and magnetic domain walls. In this way, since data can be read and written by varying the positions of the magnetic domain walls by flowing a specific current in a line type magnetic substance, a highly integrated device having a simple structure can be realized. Therefore, when the principle of magnetic domain wall movement is used, the manufacture of a memory having a very large storage capacity is possible. Examples of applying the principle of magnetic domain wall movement to a memory like RAM have been disclosed in Korean Patent Publication No. 10-2006-0013476 and U.S. Pat. No. 6,781,871B2.
However, the development of semiconductor devices that use the magnetic domain wall movement is still in the initial stages, and there are a few problems that have yet to be solved in order for them to be used in practice. One of the problems relates to reliability of the magnetic domain walls.
In order to obtain reliability in movement of magnetic domain walls, artificial notches are used. FIG. 1 is a plan view of a related art magnetic layer 200 having a plurality of notches formed therein, such as that disclosed in Korean Patent No. 10-2006-0013476. Reference numbers 20 and 25 in FIG. 1 respectively denote a magnetic domain and a magnetic domain wall. Although the magnetic domain wall 25 in FIG. 1 is depicted two-dimensionally, it is actually a three-dimensional entity.
Referring to FIG. 1, the notches are indents formed respectively in both sides of the related art magnetic layer 200, and function to pin the movement of magnetic domain walls. That is, the notches allow the magnetic domain wall to move in units of 1 bit.
However, the forming of notches in the magnetic layer having a width and thickness of only a few tens of nanometers is very difficult. It is more difficult to form notches with uniform distances, sizes, and shapes. If the distances, sizes and shapes of the notches are non-uniform, the intensity of the magnetic field pinning the movement of the magnetic domain wall (that is, the intensity of the pinning magnetic field) will vary, so that a corresponding device's characteristics are not uniform.
Also, when notches are formed parallel to a substrate, it is difficult to reduce the distance between the notches due to the limitations of an exposing process. This equates to a difficulty in reducing the bit size.
Therefore, high integration of a device and the reliable movement of magnetic domain walls are difficult to attain when notches are used.